This invention relates generally to electrical connectors and, more particularly, to an electrical connector for use in the transmission of high frequency signals.
Data communication networks are being developed which enable the flow of information to ever greater numbers of users at ever higher transmission rates. A problem is created, however, when data is transmitted at high rates over a plurality of circuits of the type that comprise multi-pair data communication cable. In particular, at high transmission rates, each wiring circuit itself both transmits and receives electromagnetic radiation so that the signals flowing through one circuit or wire pair (the “source circuit”) may couple with the signals flowing through another wire pair (the “victim circuit”). The unintended electromagnetic coupling of signals between different pairs of conductors of different electrical circuits is called crosstalk and is a source of interference that often adversely affects the processing of these signals. The problem of crosstalk in information networks increases as the frequency of the transmitted signals increases.
In the case of local area network (LAN) systems employing electrically distinct twisted wire pairs, crosstalk occurs when signal energy inadvertently “crosses” from one signal pair to another. The point at which the signal crosses or couples from one set of wires to another may be 1) within the connector or internal circuitry of the transmitting station, referred to as “near-end” crosstalk, 2) within the connector or internal circuitry of the receiving station, referred to as “ear-end crosstalk”, or 3) within the interconnecting cable.
Near-end crosstalk (“NEXT”) is especially troublesome in the case of telecommunication connectors of the type specified in sub-part F of FCC part 68.500, commonly referred to as modular connectors. Such modular connectors include modular plugs and modular jacks. The EIA/TIA of ANSI has promulgated electrical specifications for near-end crosstalk isolation in network connectors to ensure that the connectors themselves do not compromise the overall performance of the unshielded twisted pair interconnect hardware typically used in LAN systems. The EIA/TIA Category 5 electrical specifications specify the minimum near-end crosstalk isolation for connectors used in 100 ohm unshielded twisted pair Ethernet type interconnects at speeds of up to 100 MHz.
While it is desirable to use modular connectors for data transmission for reasons of economy, convenience and standardization, the standard construction of modular jacks inherently results in substantial rear-end crosstalk at high frequency operation. In particular, conventional modular jacks generally comprise a plurality of identically configured contact/terminal wires that extend parallel and closely spaced to each other thereby creating the possibility of excessive near-end crosstalk at high frequencies.
High speed data transmission cable typically comprise four circuits defined by eight wires arranged in four twisted pairs. The cable is typically terminated by modular plugs having eight contacts, and specified ones of the four pairs of the plug contacts are assigned to terminate respective specified ones of the four cable wire pairs according to ANSI/EIA/TIA standard 568. The four pairs of plug contacts in turn engage four corresponding pairs of jack contacts. In particular, the standard 568 contact assignment for the wire pair designated “1” is the pair of plug and jack contacts located at the 4-5 contact positions. The cable wires of the pair designated “3” are, according to standard 568, terminated by the plug and jack contacts located at the 3-6 positions which straddle the “4-5” plug and jack contacts that terminate wire pair “1”. Near-end crosstalk between wire pairs “1” and “3” during high speed data transmission has been found to be particularly troublesome in connectors that terminate cable according to standard 568.
When crosstalk occurs between electrically distinct circuits that are separated by a distance of much less than one wavelength, signal energy is transferred from one circuit to another either through inductive coupling capacitive coupling, or a combination of the two. For Category 5 interconnects, the shortest wavelength of interest is 3 meters, corresponding to the highest frequency of operation, 100 MHz. Since connector contact spacing in Category 5 connectors is much less than 3 meters, capacitive (electric field) and/or inductive (magnetic field) coupling will be responsible for measurable crosstalk within the connector.
Capacitive coupling will dominate when:                1) source circuits switch large voltages very quickly (large dv/dt) and/or operate at relatively high impedance levels (>>1 kΩ);        2) source and/or victim circuits have large surface areas (wide long conductors); and        3) source and victim circuits are closely spaced and separated by dielectrics (non-conductors) that increase mutual capacitance between the source and victim circuits.        
Inductive coupling will dominate when:                1) source circuits switch large currents very quickly (large di/dt) and/or operate at relatively high impedance levels (<<100Ω);        2) source and/or victim circuits enclose large loop areas; and        3) source and victim circuits are closely spaced and have their current loops oriented along parallel axes.        